Referring to the prior art drawings, FIG. 1 shows a prior art fuel injector 50. The prior art injector 50 is substantially as described in U.S. Pat. No. 5,460,329 to Sturman. A fuel injector having certain similar features may be found in U.S. Pat. No. 5,682,858 to Chen et al. The fuel injector 50 is typically mounted to an engine block and injects a controlled pressurized volume of fuel into a combustion chamber (not shown). The injector 50 is typically used to inject diesel fuel into a compression ignition engine, although it is to be understood that the injector could also be used in a spark ignition engine or any other system that requires the injection of a fluid.
The fuel injector 50 has an injector housing 52 that is typically constructed from a plurality of individual parts. The housing 52 includes an outer casing 54 that contains block members 56, 58, and 60. The outer casing 54 has a fuel port 64 that is coupled to a fuel pressure chamber 66 by a fuel passage 68. A first check valve 70 is located within fuel passage 68 to prevent a reverse flow of fuel from the pressure chamber 66 to the fuel port 64. The pressure chamber 66 is coupled to a nozzle chamber 304 and to a nozzle 72 by means of fuel passage 74. A second check valve 76 is located within the fuel passage 74 to prevent a reverse flow of fuel from the nozzle 72 and the nozzle chamber 304 to the pressure chamber 66.
The flow of fuel through the nozzle 72 is controlled by a needle valve 78 that is biased into a closed position by spring 80 located within a spring chamber 81. The needle valve 78 has a shoulder 82 in the nozzle chamber 304 above the location where the passage 74 enters the nozzle 78. When fuel flows in the passage 74, the pressure of the fuel applies a force on the shoulder 82 in the nozzle chamber 304. The shoulder force acts to overcome the bias of spring 80 and lifts the needle valve 78 away from the nozzle 72, allowing fuel to be discharged from the injector 50.
A passage 83 may be provided between the spring chamber 81 and the fuel passage 68 to drain any fuel that leaks into the chamber 81. The drain passage 83 prevents the build up of a hydrostatic pressure within the chamber 81 which could create a counteractive force on the needle valve 78 and degrade the performance of the injector 50.
The volume of the pressure chamber 66 is defined in part by an intensifier piston 84. The intensifier piston 84 extends through a bore 86 of block 60 and into a first intensifier chamber 88 located within an upper valve block 90. The piston 84 includes a shaft member 92 which has a shoulder 94 that is attached to a head member 96. The shoulder 94 is retained in position by clamp 98 that fits within a corresponding groove 100 in the head member 96. The head member 96 has a cavity which defines a second intensifier chamber 102.
The first intensifier chamber 88 is in fluid communication with a first intensifier passage 104 that extends through block 90. Likewise, the second intensifier chamber 102 is in fluid communication with a second intensifier passage 106.
The block 90 also has a supply working passage 108 that is in fluid communication with a supply working port 110. The supply working port 110 is typically coupled to a system that supplies a working fluid which is used to control the movement of the intensifier piston 84. The working fluid is typically a hydraulic fluid, preferably engine lubricating oil, that circulates in a closed system separate from fuel. Alternatively the fuel could also be used as the working fluid. Both the outer body 54 and block 90 have a number of outer grooves 112 which typically retain O-rings (not shown) that seal the injector 10 against the engine block. Additionally, block 62 and outer shelf 54 may be sealed to block 90 by O-ring 114.
Block 60 has a passage 116 that is in fluid communication with the fuel port 64. The passage 116 allows any fuel that leaks from the pressure chamber 66 between the block 62 and piston 84 to be drained back into the fuel port 64. The passage 116 prevents fuel from leaking into the first intensifier chamber 88.
The flow of working fluid (preferably engine lubricating oil) into the intensifier chambers 88 and 102 can be controlled by a four-way solenoid control valve 118. The control valve 118 has a spool 120 that moves within a valve housing 122. The valve housing 122 has openings connected to the passages 104, 106 and 108 and a drain port 124. The spool 120 has an inner chamber 126 and a pair of spool ports that can be coupled to the drain ports 124. The spool 120 also has an outer groove 132. The ends of the spool 120 have openings 134 which provide fluid communication between the inner chamber 126 and the valve chamber 134 of the housing 122. The openings 134 maintain the hydrostatic balance of the spool 120.
The valve spool 120 is moved between the first position shown in prior art FIG. 1 and a second opposed position, by a first solenoid 138 and a second solenoid 140. The solenoids 138 and 140 are typically coupled to an external controller (not shown) which controls the operation of the injector. When the first solenoid 138 is energized, the spool 120 is pulled to the first position, wherein the first groove 132 allows the working fluid to flow from the supply working passage 108 into the first intensifier chamber 88, and the fluid flows from the second intensifier chamber 102 into the inner chamber 126 and out the drain port 124. When the second solenoid 140 is energized the spool 120 is pulled to the second position, wherein the first groove 132 provides fluid communication between the supply working passage 108 and the second intensifier chamber 102, and between the first intensifier chamber 88 and the drain part 124.
The groove 132 and passages 128 are preferably constructed so that the initial port is closed before the final port is opened. For example, when the spool 120 moves from the first position to the second position, the portion of the spool adjacent to the groove 132 initially blocks the first passage 104 before the passage 128 provides fluid communication between the first passage 104 and the drain port 124. Delaying the exposure of the ports reduces the pressure surges in the system and provides an injector which has predictable firing points on the fuel injection curve.
The spool 120 typically engages a pair of bearing surfaces 142 in the valve housing 122. Both the spool 120 and the housing 122 are preferably constructed from a magnetic material such as a hardened 52100 or 440c steel, so that the hysteresis of the material will maintain the spool 120 in either the first or second position. The hysteresis allows the solenoids 138, 140 to be de-energized after the spool 120 is pulled into position. In this respect the control valve 118 operates in a digital manner, wherein the spool 120 is moved by a defined power pulse that is provided to the appropriate solenoid 138,140. Operating the valve 118 in a digital manner reduces the heat generated by the coils and increases the reliability and life of the injector 50.
In operation, the first solenoid 138 is energized and pulls the spool 120 to the first position, so that the working fluid flows from the supply port 110 into the first intensifier chamber 88 and from the second intensifier chamber 102 into the drain port 124. The flow of working fluid into the intensifier chamber 88 moves the piston 84 and increases the volume of chamber 66. The increase in the chamber 66 volume decreases the chamber pressure and draws fuel into the chamber 66 from the fuel port 64. Power to the first solenoid 138 is terminated when the spool 120 reaches the first position.
When the chamber 66 is filled with fuel, the second solenoid 140 is energized to pull the spool 120 into the second position. Power to the second solenoid 140 is terminated when the spool 120 reaches the second position. The movement of the spool 120 allows working fluid to flow into the second intensifier chamber 102 from the supply port 110 and from the first intensifier chamber 88 into the drain port 124.
The head 96 of the intensifier piston 96 has an area much larger than the end of the piston 84, so that the pressure of the working fluid generates a force that pushes the intensifier piston 84 and reduces the volume of the pressure chamber 66. The stroking cycle of the intensifier piston 84 increases the pressure of the fuel within the pressure chamber 66 and, by means of passage 74, in the nozzle chamber 304. The pressurized fuel acts on shoulder 82 in the nozzle chamber 304 to open the needle valve 78 and fuel is then discharged from the injector 50 through the nozzle 72. The fuel is typically introduced to the injector at a pressure between 1000-2000 psi. In the preferred embodiment, the piston has a head to end ratio of approximately 10:1, wherein the pressure of the fuel discharged by the injector is between 10,000-20,000 psi.
The HEUI injector 50 described above is commonly referred to as the G2 injector. The G2 injector 50 uses a fast digital spool valve 120 to control multiple injection events. During its operation, every component inside of the injector 50 (spool valve 120, intensifier piston 84, and needle valve 78) has to open/close multiple times to either trigger the injection or stop the injection during the injection event. The digital spool valve 120 has to handle large flow capacity to supply actuation liquid to the intensifier piston 78. The spool valve 120 size is relatively big and the response of a large spool valve 120 is therefore limited.
The intensifier 84 is also relatively large in mass. Therefore reversing the motion of the intensifier 84 to achieve pilot injection operation is inefficient. Once committed to compression of fuel for injection, it is much more efficient to maintain the intensifier 84 motion in the compressing stroke throughout the duration of the injection event.
Reversing of the motion of the spool valve 120 and the intensifier piston 84 results in the injection event no longer being a single shot injection, but effectively multiple short independent injection events during the injection event. Both the motion of the spool valve 120 and the intensifier piston 84 must be reversed in the duration between the pre-injection and the actual injection and reversed again to effect the “actual” injection. With such relatively massive devices as the spool valve 120 and the intensifier piston 84, this is highly inefficient.
It is believed that pilot or split injection should be injection interruptions effected during a single shot injection, e.g., with no motion reversal of either the spool valve 120 or the intensifier piston 84, but with control of the needle valve 78 opening and closing motions. As indicated above, the intensifier piston 84 has relatively large mass hence it is difficult or slow to reverse its motion.
A responsive injection system should avoid reverse motion of the intensifier 84 and, preferably, of the spool valve 120. Therefore, there is a need in the industry to utilize a mechanism to efficiently control the needle valve 78 independent of intensifier piston 84 and its controller.